Patent GB-1483475-A (GB)
Title: Pressure medium operated drive system
IPC: B60S1/10
Filed: 1974-11-29
Abstract: 1483475 Pressure medium operated reciprocating motors KNORR BREMSE GmbH 29 Nov 1974 [1 Dec 1973] 51895/74 Headings F1A, F1M and F1S A pressure medium operated reciprocating motor, preferably for operating a windscreen wiper, includes a drive piston 11 reciprocable in a cylinder 30 between first and second end positions and arranged to be exposed alternately to the action of pressure medium on a first and a second face of the piston, a changeover valve 5 movable between first and second operating conditions so as to admit pressure medium alternately to act on the first and second faces respectively of the piston, first and second control lines 12, 33 connected between the valve 5 and the cylinder and operable when uncovered by the piston moving under the action of pressure medium applied to the first or second face to communicate with the interior of the cylinder to thereby displace the valve between the first and second operating conditions, an interval switch arrangement 8 connected to the changeover valve and arranged when operated to maintain the valve in one of the first or second operating conditions whereby the piston can be maintained in a corresponding end position when it reaches the latter, the switch arrangement subsequently permitting the valve to exercise its previous control over the reciprocatory movement of the piston, a control piston 21 arranged to be brought into communication with a pressure medium source 1 when it is desired to maintain the valve in one of the conditions, and an adjusting valve 18 forming part of the interval switch arrangement 18 connected to the control line 20 and communicable with the pressure medium source 1. When the adjusting valve is displaced in use to a first operating condition under the action of a predetermined switching or control pressure the adjusting valve provides communication between the pressure medium source and the control piston 21, the adjusting valve being displaceable to a second operating condition in the event of application of reduced switching or control pressure, to provide for venting of the control line 20 through the adjusting valve. A delay arrangement 16, 23 is connectible to the pressure medium source 1 and arranged to control the application of switching or control pressure to the adjusting valve, a shut-off valve 14 forming part of the interval switch arrangement being connected to the delay arrangement and connectible to the pressure medium source. The shut-off valve is movable to a first operating condition in response to application of a predetermined switching or actuating pressure whereby the delay arrangement is vented and the pressure medium source is shut off and in the event of a reduced switching or actuating pressure is movable to a second operating condition connecting the delay arrangement to the pressure medium source 1 and shutting off the venting, the application of switching or control pressure to the shut-off valve being controllable by the pressure in the control line. By the selection of the volume of the pressure accumulator 16 and/or of the throttling of the throttle means 23 the interval or dwell time may be adjusted. Compressed air is the preferred pressure medium but compressed gases or liquid under pressure may be employed.